1. Tardigrade
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  4. Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with a speed of 20 ms-1 with respect to the ground. If an observer in car A detects a frequency 2000 Hz of the sound coming from car B, what is the natural frequency of the sound source in car B ? (speed of sound in air = 340 ms-1) :

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Q. Two cars $A$ and $B$ are moving away from each other in opposite directions. Both the cars are moving with a speed of $20\, ms^{-1}$ with respect to the ground. If an observer in car A detects a frequency $2000\, Hz$ of the sound coming from car $B$, what is the natural frequency of the sound source in car $B$ ?
(speed of sound in air = $340\, ms^{-1}$) :

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Solution:

$f =\frac{v+v_{0}}{v-v_{s}} f_{0} (v_{0} \& v_{s} $ is taken $\oplus$ when approaching each other)
$2000 = \frac{340+\left(-20\right)}{340-\left(-20\right)} f_{0 }$
$ f_{0} = 2250 $ Hz.

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